In wireless communication systems, there are a variety of reasons why a radio access network (RAN) may be unable to set up a call session with a mobile station. One of the most common reasons is that the mobile station may be out of coverage of the RAN. Another reason is that the RAN may have insufficient air interface resources to engage in call control signaling with the mobile station, such as to receive an origination message, send a page message, or the like. Still other examples may exist as well.
Although a call setup failure may occur, it does not necessarily mean that a mobile station is unavailable. Given the number of wireless local area networks (e.g., 802.11, BLUETOOTH, or other networks) that are in use today, a mobile station may often be within the coverage range of a particular WLAN and may be able to place and receive calls via WLAN communication. For instance, it is known today for a mobile station to be able to telephone connectivity via an 802.11 Wi-Fi access point. To provide such connectivity, the access point can be connected with a packet-switched network, and a media gateway system can then be provided as an interface between the packet-switched network and a traditional telephone system such as the public switched telephone network (PSTN). The mobile station can then place and receive telephone calls via a communication path comprising (i) an air interface connection with the access point, (ii) the packet-switched network, (iii) the media gateway system, and (iv) the PSTN or other telephony system.
In addition to being able to gain telephone connectivity via a WLAN access point, also known today are multi-protocol mobile stations (multi-mode devices). Such multi-mode devices are designed to exchange data wirelessly in accordance with more than one protocol. For example, one protocol may be a wireless wide area network (WWAN) protocol such as CDMA, TDMA, AMPS, or GSM, and the other protocol might be a WLAN protocol such as 802.11 or BLUETOOTH. If communication according to one protocol is not available for some reason, the device may then communicate via the other protocol instead.